Quasi-stationary waves in the southern hemisphere: observations and climate simulations over South America / Ondas quase-estacionárias no hemisférico sul: observações e simulações climáticas sobre a América do Sul

AUTOR(ES)
DATA DE PUBLICAÇÃO

2004

RESUMO

Characteristics of the quasi-stationary waves in the Southern Hemisphere with emphasis on their behavior over South America are discussed. In the first part, an observational study is performed using the NCEP/NCAR reanalysis data. The nature of seasonal and inter anual variabilities is analyzed. A comparison between the of the quasi-stationary wave s amplitudes and phases betweenthe 1950-1998 and 1979-1998 periods data showed that the differences are not large and the 49 years data can be used for the study. It is found that the amplitude of wave 1 is high and the waves 2 and 3 have much less amplitude. The wave 1 shows two maxima, one at high latitudes in the stratosphere in the austral spring and the other at sub-tropics in the upper troposphere in the austral winter. A comparison of the Eliassen-Palm fluxes between the EI Nino and La Nina events showed that during the EI Nino a stronger upward and equatorward propagation (energy) of the quasi-stationary waves occurs, particularly in the austral spring. To examine the quasi-stationary wave propagation Plumb s methodology is used. During the EI Nino and La Nina events a c1ear wave train can be identified at 300 hPa in all seasons except in summer and centers of positive (negative) anomalies of geopotential in the austral spring over the southeast Pacific near South America, favors (disfavors) the occurrence of blocking highs in this region. In the second part, a modeling study is perfomated using the ETACLIM and RegCM3 regional c1imate mo dels to simulate the quasi-stationary circulations (Bolivian High) over South America in the austral summer. The effects of global anomalies (EI Nino 1997/1998 and La Nina 1998/1999) over the region were examined. The validation of simulations of the c1imatology of January (1991-2000) in both models showed similar skill. However, the simulations of upper and lower levels circulations and precipitation fields of ETACLIM were better that of the RegCM3. Both models are able to simulate the interanual variability during ENSO events with success. The quasi-stationary anomalies were filtered (total and partial) in the integrations of both mo dels during this events. In the southeast of continent, the Amazonian and north of Peru regions showed great sensitivity to these anomalies and others regions the signal was less evident. These results showed the relative role of quasi-stationary waves over South America.

ASSUNTO(S)

south america dynamics climatology climate model ondas estacionárias regional model modelo climático américa do sul stationary climatologia dinâmica modelo regional waves

ACESSO AO ARTIGO

Documentos Relacionados